The girls' powers are as follows: Cleo can manipulate water, Emma can freeze water, and Rikki can boil water. In Season 2, they gained weather control as well. Cleo can manipulate wind, Emma can now draw moisture from the air to freeze and Rikki can draw forth lightning which catches things on fire.
Nickelodeon advertised a 15 minute sneak peek two weeks before the show was aired.
Cariba Heine hired a professional trainer to help improve her swimming while auditioning for the part of Rikki.
The actresses put full cream milk in their eyes to help them keep their eyes open underwater.
The mermaids' wardrobe frequently follows a color scheme. Emma: white/blue, Cleo: pink/purple, Rikki: black/red.
First appearance of the mysterious Elder (later revealed to be Louise Chatham).
Ashleigh Lawrence, who plays Emma's guest Alyssa, later appears in the series as the elder Mermaid Gracie.
The text on the Mermaid website Lewis is researching is heavily drawn from Anthony Piccolo's article 'Women of the Deep: A Light History of the Mermaid', originally published in 'Sea History' #68, Winter 1993-4.
Rikki's first rescue, and the first time any of the mermaids performed a rescue. She risked exposure as a mermaid on a public beach and rescued Emma's brother Elliot.
The Mermaids' 'allergy' to moonlight is established.
This episode reveals that Emma's mother, Lisa Gilbert, saved Zane's father, Harrison Bennett, from drowning when they were both about 12 years old.
Rikki's second rescue, though technically more of an assist. She protected Zane Bennett from shark attack while Lewis rescued him on the surface.
The boat central to this episode is named Lorelei, which is the name of a Mermaid-like girl in a German legend; the beautiful Lorelei was desired by all men except her one true love. Eventually forced to become a nun for her alleged lechery, she ultimately glimpses her love from a cliff over the Rhine and leaps over. In death Lorelei becomes a Siren, whose captivating song lures sailors to their death.
Emma's first rescue: She rescued Zane Bennett from certain drowning in the sunken wreck. Emma was also the first one of the three whom Zane saw as a mermaid. This is also significant in that Emma's 50 year counterpart, Louise, is the only one of those three known to have performed a marine rescue.
Cleo's sixteenth birthday is established as Apr 19, 2006. Since it is fairly self-evident that the first few full moons in the series are consecutive (the first two certainly are), some dates can be implied by back-tracking full moons. This would make Cleo's "siren" experience to be Fri Apr 14, 2006. Neil Gilbert's 50th birthday and Emma's moon-fever experience, Wed Mar 15, 2006. If that date is correct, then it is proven that Cleo, Rikki and Emma became mermaids under the full moon of Mon Feb 13, 2006; (actually the following morning).
The Gold Coast (where the series is set) saw a total lunar eclipse on the evening of 28 August 2007, just over a month before the premier of the show's second season. Some fans use this to set the dates for events in the series.
This is the only time in the first three seasons that one of the mermaids was injured underwater by normal stuff, proving therefore that they can be. Rikki was hit on the head by a sinking crate and knocked unconscious. Zane rescued her, making the first and only time in the first three seasons that one of the mermaids was rescued by a non-mermaid. Rikki was still unconscious after changing back, and still had the cut on her forehead.
The title is based upon a quote from William Shakespeare's play "Macbeth" (Act IV, Scene I): "Double, double toil and trouble; Fire burn, and cauldron bubble."
Sophie Benjamin bears an uncanny likeness to the mermaid Julia from 50 years ago, because Taryn Marler played both parts.